JPS63307129A - Production of optical element - Google Patents

Abstract

PURPOSE:To prevent surface defects such as burning or attachment of foreign matter in production process, by carrying out surface treatment in cooling process of molten glass material after press molding in a given temperature range <= the lower limit point of strain removal. CONSTITUTION:A molten glass material is molded by using a mold device for molding. Then the molded article after molding is slowly cooled. In the cooling process, the molded article is subjected to surface treatment in a state wherein the temperature of the molded article is in the lower limit point of strain removal - 200 deg.C to form a thin film. Consequently, an optical element which has optically functional face with excellent durability free from surface defects is obtained in high yield.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing optical elements such as lenses, prisms, mirrors, and filters, and in particular to a method for manufacturing optical elements such as lenses, prisms, mirrors, and filters, and in particular, a method for manufacturing optical elements such as lenses, prisms, mirrors, and filters from molten glass material without undergoing processes such as grinding and polishing. The present invention relates to a method for efficiently manufacturing, at low cost, an optical element having an optically functional surface with good surface precision and durability using press molding.

[Prior Art] Generally, optical elements such as lenses, prisms, mirrors, and filters are manufactured by grinding a glass material to give a desired external shape, and then polishing the functional surface, that is, the surface that transmits and/or reflects light. It is manufactured by forming an optical surface using

However, in the production of optical elements such as those described above, in order to obtain the desired surface accuracy (i.e., accuracy of surface shape and surface roughness) through grinding and polishing, skilled workers spend a considerable amount of processing time. It was necessary to do it. Furthermore, when manufacturing an optical element whose functional surface is an aspherical surface, more advanced grinding and polishing techniques are required, and the processing time is inevitably increased.

Therefore, recently, instead of the traditional optical element manufacturing method as described above, optical element materials are housed in a molding mold device with a predetermined surface accuracy and pressed by heating and pressurizing. Increasingly, the overall shape including the functional aspects is immediately formed by molding. According to this, an optical element can be manufactured relatively easily and in a short time even when the functional surface is an aspherical surface.

In the method of manufacturing an optical element by forming an optically functional surface by press molding, a preform is obtained by making an optical glass material into a shape approximating the desired shape. There is a method in which the molten optical glass is placed in a mold device and pressed into a final 1'' shape, and a method in which the molten optical glass is immediately placed in a mold device and pressed and molded.

In the method using preform, the Japanese Patent Publication No. 61-3226
As described in Publication No. 3, a preform is obtained by an appropriate method such as grinding and polishing, and the preform and the mold member of a mold device for final molding are placed separately or the preform is housed in the mold device. It is necessary to heat the preform to a predetermined temperature in the state, press the thus softened preform with an appropriate pressure in a mold device, and allow it to cool.

However, since this method requires the same steps as the conventional traditional method to obtain the preform, it is still not fully satisfactory in terms of manufacturing cost.

On the other hand, a method in which molten glass is directly housed in a molding device and press-molded reduces the time required for the process and is particularly suitable for continuous molding.

By the way, in optical elements press-molded as described above, an anti-reflection film is generally applied to the functional surface by vacuum evaporation method etc. for the purpose of improving the functionality of the optical function or improving durability. In many cases, a surface treatment is performed to coat the surface with a reflective film or a reflection-enhancing film.

Conventionally, such thin film forming surface treatment was carried out by once cooling the molded product obtained by the above-mentioned press molding to near room temperature, and then transporting the molded product into a surface treatment equipment and heating it to an appropriate temperature. It's being done above.

However, in the conventional method for manufacturing coated optical elements as described below, it takes a considerable amount of time from the time the molded optical element is taken out of the molding device until the actual vapor deposition. The carbon dioxide gas and moisture inside may act on the molding surface and cause discoloration, and foreign matter such as dust often adheres to the molding surface of the molded optical element, so a cleaning process is performed before the vapor deposition process. However, since the cleaning process also exposes the product to the cleaning liquid, the frequency of occurrence of burns increases.

As described above, in the conventional method V:, the optical functional surface tends to be discolored during the process before vapor deposition, so there is a problem that the incidence of defective products increases depending on the type of glass material. Furthermore, there are some types of glass that, despite having characteristic optical properties, are practically unusable due to the above-mentioned tendency to cause significant fading.

Furthermore, in the conventional method described above, the press-formed product is first cooled to near room temperature and then reheated for surface treatment, resulting in a large loss of thermal energy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to stably manufacture a surface-treated high-precision optical element with good efficiency and low energy consumption.

[Means for Solving the Problems] According to the present invention, the above objects are as follows: Press-molding a molten glass material using a molding device,
An optical element characterized in that when the molded product thus obtained is cooled, a surface treatment is performed on the molded product when the temperature of the molded product is between the lower limit of strain removal and 200°C. This is achieved by a manufacturing method.

[Example] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a graph showing changes in glass temperature over time to explain a first embodiment of the optical element manufacturing method according to the present invention. Incidentally, FIG. 1 also shows the case of the conventional method for comparison.

FIG. 2 is a diagram showing the optical element 2 manufactured in this example, and the optical element is a biconvex lens with a first surface having a radius of curvature of 52 mm and a second surface having a radius of curvature of 40 mm.

Note that this example uses P bo- which is known as a low melting point glass.
B203=Z This relates to the case where a glass containing no as a main component is used.

FIGS. 3 and 4 are explanatory diagrams of press molding by the molding device in this embodiment.

In these figures, the molding device has an upper mold member 12 and a lower mold member 14, and the lower surface of the upper mold member has a molding surface having a shape corresponding to the first surface of the optical element 2. 12
A is formed on the upper surface of the lower mold member 14, and a molding action surface 14a having a shape corresponding to the second surface of the optical element 2 is formed.
is formed. The surface roughness of these forming working surfaces 12a, 14a is made to be equal to or less than the surface roughness of the optically functional surface of the target optical element (mirror finish), for example, RmaxO,01 m or less.

The upper mold member 12 and the lower mold member 14 are each moved in the vertical direction by a drive source (not shown), thereby opening and closing the mold.

Although not shown, the mold device is equipped with an appropriate heating means, and the heating means can control the temperature of the mold member and the glass material to a desired temperature.

In the above mold device, the upper mold member 12 and the lower mold member 14
When the mold members are closed, the molding working surfaces 12a, 14a of both mold members
The shape of the cavity formed in between is such that it becomes the final lens shape shown in FIG.

FIG. 3 above shows the process of supplying molten glass to a mold device.

In FIG. 3, 33 is a glass melting tank (crucible), and a heater 34 is attached around the crucible. An outflow section 36 is connected to the lower part of the crucible 32, and a heater 38 is attached around the outflow section. and,
A cutter 40 is arranged below the outflow portion 36 to cut the continuously flowing molten glass into appropriate lengths.

A raw material for a desired optical glass is placed in the crucible 33, and heated to an appropriate temperature by operating the heater 34. This results in
Molten optical glass G is formed in the crucible 33. Incidentally, at this time, by appropriately stirring and performing defoaming treatment as necessary, an optical glass with higher homogeneity can be obtained.

The molten glass gradually flows down within the outflow section 36 under the action of gravity and is pushed out from the outflow port at the lower end of the outflow section. At this time, the lower mold member 14 of the mold device is placed below the outlet.

The molten and softened glass is pushed out from the outlet of the outflow section 36, and when its tip reaches an appropriate height below the cutter 40, the cutter is activated to cut the molten glass.

The thus cut glass block 4 falls onto the molding surface 14a of the lower mold member 14 at time t1.

The above-mentioned FIG. 4 is a diagram showing the state at the time of pressing.

As shown in FIG. 4, the lower mold member 14 on which the glass block 4 is mounted is carried to a position corresponding to the upper mold member 14, and is placed at a temperature of 370° C. from time t2 to t3. Press the mold member 12 to close the mold and perform molding,
A molded article 6 having the desired final shape is obtained. - After the above-described molding, cooling is performed. The cooling.

This is achieved by controlling the amount of heat by the heating means of the mold device.

Cooling is performed until the molded product 6 reaches the lower limit temperature for removing strain (glass has a viscosity of 101
The molded product is housed in the mold device until the temperature reaches 300°C (temperature showing 45 poise) and is carried out relatively slowly from time t3 to t4, and after the temperature reaches below this temperature, comparison is made from time t4 to t5. Cool at the highest rate possible. This is because if cooling is performed too rapidly above the strain removal lower limit temperature, internal strain will occur, and this strain will not be effectively removed below the strain removal lower limit temperature. Since internal strain does not substantially occur below the strain removal lower limit temperature, there is no problem even if the material is rapidly cooled.

Before the temperature reaches 200° C., the mold device is opened, the molded product 6 is taken out, and the molded product 6 is carried into the vacuum evaporation device to start vacuum evaporation. For example, as shown in FIG. 1, the molded product is transferred from the mold device to the vacuum deposition device between time t4 and t5, when the temperature reaches 250°C, and between time t5 and 70, the molded product is transported into the vacuum deposition device. MgF2 is vacuum-deposited on the optically functional surface.

Thereafter, the coated optical element is removed from the vacuum deposition apparatus and cooled to room temperature.

In order to carry out the series of press forming, cooling and vacuum deposition processes continuously and efficiently, the press forming and cooling described in 1-1 are carried out in a vacuum, and the vacuum vapor deposition equipment is placed in the same vacuum system. It is preferable to do so. However, it is preferable to provide a gate pulp between these devices so that the valve is opened only when an optical element is transported.

On the other hand, in Figure 1, the dotted line indicates the process of press forming, cooling to room temperature, cleaning, carrying into a vacuum deposition equipment, heating, vacuum deposition, and cooling using the conventional method of press forming using a preform. An example in which an optical element similar to the above embodiment of the present invention was manufactured will be shown.

As can be seen from FIG. 1, in the conventional example, the time required for the cooling process from time t5, the cleaning process, and the reheating process before vapor deposition (i.e., from P1 to P2) is longer than in the embodiment of the present invention. Moreover, the energy loss is greater than in the embodiment of the present invention by the amount of heat energy consumed during this time. Therefore, according to the embodiment of the present invention described above, considerable cost reduction is possible.

Furthermore, according to the embodiment of the present invention, vacuum evaporation is performed immediately after cooling after molding, without a long delay, so that there is no possibility that foreign matter such as dust may adhere to the optical functional surface before vacuum evaporation. Therefore, unlike the conventional example, the present invention does not require a cleaning process, and due to this and the short time until vacuum deposition, it may come into contact with the cleaning liquid, air, etc. and cause burns. There's nothing like it.

” - The optical element obtained in the example of the present invention was heated at a temperature of 30°C.
When the sample was stored in an atmosphere with 100% humidity for one month, no optical defects such as clouding were observed on the optical functional surface.

On the other hand, in the case of the conventional example described above, discoloration was observed after the cleaning process, and partial defects were observed on the optical functional surface after vacuum deposition.

As described above, according to the embodiments of the present invention, it is possible to obtain a good optical element using glass, which was not able to be obtained by the conventional method due to insufficient chemical durability.

FIG. 5 is a graph showing changes in glass temperature over time to explain the second embodiment of the optical element manufacturing method according to the present invention. Incidentally, FIG. 5 also shows the case of the conventional method for comparison.

This embodiment differs from the first embodiment only in that fine annealing for fine adjustment of the hN refractive index is performed after vacuum deposition.

In this embodiment, fine annealing is performed immediately after the first vapor deposition. The annealing is performed at a temperature higher than the deposition temperature for a desired period of time (maximum temperature 320° C.).

On the other hand, in FIG. 5, the dotted line indicates an example in which an optical element similar to the embodiment of the present invention was manufactured by further performing cleaning, heating, and fine annealing steps following the conventional example shown in FIG.

As can be seen from FIG. 5, in the conventional example, the cooling process from time t5, the cleaning process, and the reheating process before vapor deposition (that is, from P1 to P2), the cooling process after vapor deposition, the cleaning process, and the reheating process after vapor deposition. The heating process (that is, from P3 to P4) takes more time than in the embodiment of the present invention, and the energy loss is greater than in the embodiment of the present invention by the amount of heat energy consumed during this time. Therefore, according to the embodiment of the present invention described above, considerable cost reduction is possible.

In the embodiment of the present invention shown in FIG. 5, vacuum evaporation was performed before fine annealing, but it is also possible to first perform fine annealing and then perform vacuum evaporation during the cooling process. According to this, thermal energy loss is further reduced and costs can be further reduced.

[Effects of the Invention] According to the present invention as described above, when the temperature of the molded product is between the lower limit of strain relief and 200°C in the cooling process after press forming, the surface of the molded product is immediately applied. Since we will process
It is possible to sufficiently prevent surface defects such as fading and foreign matter adhesion during the manufacturing process, making it possible to manufacture optical elements using glass, which was previously unsuitable for manufacturing optical elements due to its low chemical durability. In addition, surface-treated optical elements can be stably manufactured with good efficiency and low energy consumption.

[Brief explanation of drawings]

FIGS. 1 and 5 are graphs showing changes in glass temperature over time to explain the method for manufacturing an optical element according to the present invention. FIG. 2 is a diagram showing the optical element. FIGS. 3 and 4 are explanatory views of press molding using the molding device of the present invention. 4 Ni glass block, 6: Molded product, 12 2 Upper mold member, 14: Lower mold member, 33 Niru crucible, 36
:Outflow part. Agent: Patent Attorney Seki Yamashita, Figure 7, Figure 3, Figure 4

Claims (4)

[Claims] (1) When the molten glass material is press-molded using a molding die device and the molded product thus obtained is cooled, the temperature of the molded product is between the lower limit of strain relief and 200°C. Characterized by performing surface treatment on molded products,
A method for manufacturing an optical element. (2) The method for manufacturing an optical element according to claim 1, wherein the surface treatment is a thin film forming treatment in terms of optical function. (3) The method for manufacturing an optical element according to claim 2, wherein the thin film is formed by CVD or PVD such as vacuum evaporation or sputtering. (4) The optical element according to claim 1, wherein the molded product is subjected to fine annealing when the temperature of the molded product is between the glass transition point and the lower limit point of strain removal when the molded product is cooled. manufacturing method.